Clinical studies related to cardiac pacing have shown that an optimal atrio-ventricular delay (e.g., AV delay) and/or an optimal interventricular delay (e.g., VV delay) can improve cardiac performance. For example, given an optimal VV delay, cardiac resynchronization therapy (CRT) can deliver electrical stimulation to the heart at a right ventricular site (e.g., apex or interventricular septum) and then deliver electrical stimulation to the heart at a left ventricular site (e.g., postero-lateral wall) to improve mechanical dyssynchrony associated with an intrinsic abnormal ventricular activation pattern (e.g., due to left bundle branch block). With respect to AV delay, simply setting a CRT device's AV delay to a value less than a patient's intrinsic conduction time (i.e., to reduce competition from intrinsic activity with delivered electrical stimuli to the ventricles) is not necessarily optimal as results from the DAVID trial indicate that an excessively short AV delay can cause potentially detrimental, unnecessary ventricular pacing. Similarly, an overly long AV delay can be as counterproductive as an overly short AV delay for patients with intact nodal AV condition. Indeed, a truly optimal AV delay may cause CRT to deliver optimal intermittent ventricular pacing (i.e., an AV delay that is not too short and not too long).
Optimization of an AV delay and/or a VV delay often occurs at implantation. However, what is “optimal” for an AV delay and/or a VV delay depends on a variety of factors that may vary over time. Hence, sometimes, re-optimization of a delay or delays occurs during a follow-up consultation. While such optimizations are beneficial, the benefits may not be long lasting due to changes in various factors related to device condition, cardiac function, patient behavior, etc. Such factors may change unpredictably between consultations. Further, as the period between consultations increases, the chances that a patient's CRT is using suboptimal delays increases.
As described herein, various exemplary methods, devices, systems, etc., aim to determine and/or adjust AV delay, VV delay and/or other inter-chamber delays. Particular techniques involving such delays are presented for intentional fusion where one ventricle can be activated via an atrial to ventricular conducted depolarization and where the other ventricle is activated via artificially delivered electrical stimulation. Such techniques may use an optimal AV delay that is neither too short nor too long and that allows for intermittent ventricular pacing.